Whither West Nile?

Wednesday, April 22, 2009

In the past few years, the health-threat phenomenon in the Midwest, the mosquito-borne West Nile virus, is among the most unbelievable situations confronting public health in a long time, according to experts, who say they're shocked at how quickly it had spread across the country.

Iowa State University entomolgists have been tracking mosquitoes and the illnesses they cause since 1968. "We were extremely fortunate to have a mosquito monitoring program already in place in Iowa," said an ISU entomolgist. "When West Nile hit, we were ready to go."

The West Nile virus first appeared in New York City in 1999. It spread to six states by year 2000, was first detected in Iowa in 2001, and now has spread all the way to California and Washington state.

The virus has been found in humans, horses and birds. Most people infected with the virus don't get sick. But one in 150 people will develop a severe form of the disease.

Rural and urban residents have reported thousands of dead birds the past few years, assumed to be victims of the virus. What impact might this have on the avian food chain?

Iowa's mosquito monitoring program began 40 years ago because a child in Wisconsin died from a mosquito-borne illness.

Each June, a flock of 10 chickens is stationed in 12 counties around the state. Local health department personnel draw blood samples from the chickens every 10 days, sending the samples to the state lab in Iowa City for testing. Some of the chickens have developed antibodies to West Nile. When antibodies are detected, it proves the birds have been bitten by mosquitoes carrying the virus.

Mosquito traps also are placed in the same communities. Health department officials check the traps five days a week. Mosquitoes trapped are then sent to the lab at ISU to be identified and tested.

Mosquitoes also are collected twice each month from a second type of trap. These are sent to ISU for identification and then to Iowa City to check for viruses. There are 54 species of mosquitoes in Iowa. To date, the state monitoring program has uncovered three species carrying West Nile virus.

Experts thinks the prevalence of West Nile virus will decline over the next few years. There won't be near the number of horses infected next year because most have now been vaccinated in Iowa.

Also, infected birds that survive will develop some resistance to the virus and pass that to their offspring, which will result in fewer infected birds and less chance of mosquitoes spreading the virus from birds to humans.